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Nov. 22, 1927. 1,649,901 A. HOUGH METHOD OF AND APPARATUS FOR MAKING NITRIC ACID Filed March 27 1925 s Sheets-Sheet 1 Exhaust!- Condenser Wafer- Dre/'0 I'NVENTOR:

#22: A TTORNEY.

Nov. 22, 1927. 1,649,901 A. HOUGH METHOD OF AND APPARATUS FOR MAKING NITRIC ACID Filed March 27- 1925 3 2,

W 2. Exhaust" C'Oadeaaer ponifr'l'c Z/eael er I owe" INVENTOR.

Nov. 22, 1927. 1,649,901

A. HOUGH METHOD OF AND APPARATUS FOR MAKING NITRIC ACID Filed March 27. 1925 s Sheets-Sheet 3 Hypon l fl'lc 75am- 34v cook INVENTOR.

6% TTORNEY.

Patented Nov. 22 1927.

UNIT TA imrnun'nouon, or suiuiurr, NnwJ-EasnY, Assamese zrrinjnunrnoncoMrANm, r mo o]? NEW YORK, s. Y., A COBBORATION 0E NEW i METHOD or arm APPARATUS-FOR nexme NITRIC ACID.

' App1ication filed March 27,1925. Ser ano. 18,723; f

This invention relates toimprovements in the production of nitric acid and hasfor its principal oh'jects'the economical production of nitric acid of a high degree of purity and strength and the provisionot'an apparatus.

for such production which is extremely economical in original cost and in operation and maintenance, besides being highly efi'ective" and compact. V

In the production of nitric acid from the reaction ot sodium nitrate or its equivalent and sulphuric acid, it is a desideratum that thetwo ingredients should be maintained from the very start or the operation in a most intimate state of admixture, furthers Ymore, that the exposed surfac'e'of the liquid i should be 'a'sfextensive as possible in order to permit of the most e'flicrent evaporation of the vapors and also that the still in which the reaction is being carried out should he so mounted as to j'perniit of-theperfect regulation of the temperature thereof,particularly of the upper portion thereof in order to pro vent both condcnsationf and decomposition of the nitric acid raporseither under low temperatures or abnormally high temper atures.

The aforesaid conditim s while highlyde sired in'good nitric acid; plants are, at the" present time, not even approached either in plants employingthe oldpot type of still or in the vacuumtype of plant, but in my improved type jo'tnitr cacid plant," as hereinafter described, it is possible to maintain the aforesaid conditions and to comply with the aforesaid desired requirements of an ideal plant in the most satisfactorymanner whereby it'is possible to construct a plant capable ot the production of nitric acid of the high est degree of purity and strength in a minimum time of operation, and consequently at a minimum price "with but a very small ini tial capital investment.

. 'In the accompanyingdrawings forming a part of this specification, I have illustrated a plant embodying thepreferred form of my invention. In said drawings I Figure l is affront elevation; Fig. 2is' a side elevation i Fig. 13 is a planview of a portion of a Figs. 4 and 5 are detail plan and section I of one of the discs employed, respectively.

Reterringfto the drawings and the con- .struction shown therein, reference numerals '1, 1 designate :the' two sections comprising a duplex nitric acid still of the horizontal.

"type which is ed in two sections, the lower section being provided with a discharge conduitQfor the removal of nitre 'cakeand having stuffing boxes 3, 3' mounted in the respective ends thereof, which latter serve to receive a shaft 45. Such shaft" is supported at. each end in"bearings"5, v 5. mounted 'in'suitabl'e biacketsfiffi and said still is supporte'd in the customary manner brackets 'of"suitable brick work mounted as designed by'the reference numeral a. "The upper section 1" of the stillis' provided with a'Yvapor' outlet 7, fiDF aClddIIlGt conduit 8 and an aperture 9 througnwliich the charge of sodium'nitrateor its equivalentis introduced into the still. -Mounted on the said shaft 4:, which preferably consists of close grain cast iron; having a steel-core,1is a series ofdiscs' 10, provided With-perforations 11,".preferably' of cast iron; These perforated discs perform a dual; function ofmixing and evaporating units since the discsare adapted? to serve as very efiicient agitators whilethe mass is in a liquid phase andcut theirway through the mass as it assumes a solid, phase continuing so long as the mass remains in this latter state buta-lso as the soft or fluid phase again develops, the perfo'-- rated discs will "pick up, the mixture and resume the normal agitation function; If desired, in lieu of the perforations, discs 10 may he provided with radial groove'sr'or otherwise ribbed or roughened in order to admit of the same serving as effective mixers or agitators asaforesaid. l 7

'The lower sectionl of said still as shown slopes towards the intro cake discharge conduit 2 and is provided with a well 12 which extends parallel with such shaft 4 and at right angles to said discs 10 which is adapted to receiveany solid nitre cake,-thus preventing the samebeing se'izedor picked up by thediscs f Said sections of the still are mountedin a flue of a furnace which may be of any suit- I able type, the gases from which pass under the still and some go over the top of the upper section'of the still. A damper 14 is disposed withintheoutlet'pipe 13-from the said flue in, such a manner that the temperatures of thefgases which passover the upper section of the still can be readily adjusted vapors which would create a condition disastrous to the life of thestill cover and also to prevent decomposition of the strongest nitric acid which vis very sensitive to heat, due to over heating the same, thus enabling the latter acid to be recovered along with the other strength of acid with the result that the blend of the various strengths will be increased. i

A bleacher 15 provided with a jacket 15 is interposed between a condenser 16, the latter being of the reflux type, and the vapor outlet 7 of the upper section 1 of the still, such bleacher serving to eliminate the lower oxides of nitrogen from the nitric acid and delivering water-white acid to receivers 17, the lower oxides of nitrogen passing into oxidizing towers 18, wherein they are admixed with the water and air and converted to nitric acidin the usual way. The aforesaid bleaching action is based on the principle of low solubility of lower oxides ofnitrogen in hotnitricacid and the ready solubility of the same low oxides of nitrogen in cold nitric acid. This principle is utilized by the passage of the hot nitric acid vapors from the vapor outlet to the base ofthe bleacher, thence upwardly through the reflux condenser wherein the colder nitric acid is refluxed back into the bleacher and therein meets hot nitric acid vapors, with the consequence that theliquid nitric acid is thus maintained at a temperature approximating its boiling point at which temperaturethe low oxides of'nitrogen are practically thrown completely out of the solution of nitric acid and pass completely through the system to the hyponitrous oxidizing towers.

Since the functioningof the bleacher is dependent upon the maintenance of both it and .the nitric acid distillate entering the same at a high temperature, otherwise as is apparent from .the foregoing explanation, were the bleacher cold, the first runnings of nitric acid obtained would contain .a considerable percentage of low oxides of nitrogen which would be highly undesirable.

The strength of the sulphuric acid and the relative amount of sodium nitrate and sulphuric acid'which are employedin the opera tion of the still will vary according to the local conditions and the p 'upose for which the nitre cake is to be utilized. Inthose cases where a maximum strength of the nitric acid blend is desired, it is advisable to employ sulphuric acid of 96% I-I SO content and a substantially dry sodium nitrate. In those cases where a weaker-nitric acid only is required, then it is possible to employ sulphuric acid of a weaker content and normal damp sodium nitrate of the ordinary moisture content.

soda, the same is first placed in the stills and, while the discs are rotating, a low degree of heat is applied to the still. The thorough agitation that the nitrate of soda is therein subjected to, together with the gentle heat employed, will evaporate the water from the sodium of nitrate which will, of course, be condensed in the main condenser, and flow out through the outlet 6 of the said condenser. Such water distillate is prevented from entering the main nitric acid receiver by means of a bypass of any desired form and is usually discarded. When the water ceases to be given off from the sodium nitrate in the still, the sulphuric, acid is introduced into the still and the reaction resulting in the production of the nitric acid commences.

If the temperature of the sulphuric acid entering the still is extremely cold, as would ordinarily be the case in cold weather, particularly in large plants, it will have a tendency to'crack the heated still which, of course, would be a matter of serious moment.

It is preferred, therefore,. to heat such acid tube heating unit 19 (preferably of cast iron) is positioned in the stack 1-3, wherein there is ample waste heat for this purpose and this heater isemployed to preheat the sulphuric acid in its passage to the still. Through this arrangement it is possible to easily raise the temperature of the sulphuric acid to a safe temperature to pass into the still, for example about 80 0., which teinperature moreover is sufiicient to induce instant or immediate distillation of the nitric acid upon the contact of the sulphuric acid with the charge of sodium nitrate previ ously introduced into the still.

The reactions ocurring between the nitrate ofsoda and the sulphuric acid employed are somewhat complicated, the mass passes through several phases; for example, when the mixture is first heated up there is a quantity of acid vapors evolved, but after av short time the mass enters into the solid phase. In this latter condition .it has been found to be extremely diiiicult, if not impossible, to accomplish cii 'cctive agitation by means of an ordinary propeller type of agitator and at the best but a small portion of the mass while in a liquid phase could be agitated by such a propeller." When the mass, however, became solid or even the heavy viscous phase developed, such a propeller would bind and become perfectly useless. ith my improved disc type of agitator herein described, the disc continues to function irrespective of the condition of the mass within the still, for example, when the solid phase develops, the disc-simply cut their way through the solid mass and continue to rotate without interruption until seiner such time as the softer fluid phase has developed, whereupon they will, as previously stated hereinpcontinue' to seize or pick up thennixturefand to function normally.

q els m mounted,isrelieved' 'of all strain or wear by means oft he bracket b6fll'il'l 'S5 and one end of such shaft is cause to project sufiicientlyfbeyond the still to permit of the gears-Q QI being attached thereto, which latter is adapted tobe connected to a driven gear in a train of power operated gearing in the vellknown manner. a

The functioning of the foregoing apparatus isso complete that the'quantity of acid produced inthe oxidizing "towers-(is so small that it can be charged into the still.

, tent of the initre cake; horexample, it has with the suc ceedingj charge: of nitrate, of soda andsulphuricjacid andv distilledover asst'rong acid without such addition of acid unduly raising the sulphuric acid con been ascertained that the amount of low the old qi'l'antityof-"the flue gases which have passed oxides o't nitrogen resulting from the reactions" in this improved .type' of still ainountsto only about of the total nitric acid} represented in thenitrate soda. in po "type ofstill, this, "percentage averages aboutflilffi) to 15%; a a

The aforesaid'jdamper 1 4i" is so arranged within the pipe] 13 "that predetermined over theupper section of thesti'll can be mixed with the stack gases," thereby lower ing the ten'iperature ot 881d flue gases to the point required to heat the upper section:

1"" of still to the requisite degree net-cs5 sary to preventcondensation of the nitric acidvapors ,and decomposition of the strongest'nit clacidas hereinbefore stated "In the" production of nitric' acid by my aforesaid invention, the agitated mass is continuouslymaintained ,in the form of a film; the charge in the still is not only constantly agitated, but is converted'into a plu rality'of films which are'peculiarly eflicient for permitting ofthe freeescape of the nitric acid vapors while the mass is still at a comparatively; low temperature by virture of the extremely large surface which is afforded by thefilrns for this purpose. for example, by the employment-of the aforesaid discs, it

' is possible in practice to aiford a film evapo rating; surface haiing some fifteen times the total interior surface of the still; Furthermore, the perfect regulation of the temperature of the still, particularly of the upper section thereof, resultsin not only greatly prolonging the lifeof the still, but also in greatly reducing the proportions of the nitri acid or lower oxides of nitrogen resultring from the decomposition of'the strongest nitric acid which passed to the oxidizing towers.

- Heretofore, 1n the best IlltllCflCld plants,

ifupon whichith'e' discs 10 are 7 production of nitric acid iti-has been impossible to attain or even approachthe ideal conditions herein de-- scribed as attainable by my'invention, and

yall'attempts to attain the same by means of a vacuum type f plant, however m d have resulted in failure. y r a The coil 19 and the pipe connecting same to pipe 8, while shown in dotted lines as indicating that same, may be omitted, is preferably employed, as, thereby the waste heat is most effectively utilized, a matter of which is of no inco-nsiderable moment-in the I Preferably in orderto further conservethe heat of the flue gases'or other heating medi-' um introduced into the jacketl5, thesame is insulated with'he'at insulating material,

aasmagnesia,asbestosor'the like. r

1 lVhile'I have described the preferred typ i of apparatus in which my improved I method,

aspre'ferably shown can be'carriediouh it is,

of; course, understood,- without departing from the spirit of my invention, that various modifications both in the method and apparatus' herein described within the scope of the appended claims can be ma'de without departing from the spiritfof myinvention as covered by such claims.

Having thus describedmy invention, what I claim anddes'ire to obtain by United. States Letters Patent is; Y v

1; lllethed' of making nitric acid which consists in'subjecting a reacting mass including: sulphuric acidand a nitrate capable of yielding nitric acid vapors when heated, to

a distilling temperature while constantly agitating' the mass being treated and causing separate portionsof the'same to be simultaneously presented in theform of separate films to permit of the free escape of acid vapors therefrom at comparatively low I tem' peratures and then recovering the nitric acid evolved from such treatment. I r

2.1 Method of making nitric acid which 'con'sistsin subjecting a reacting mass comprising an alkali-metal nit-rate and concentrated sulphuric acid capable of yielding nitric acid vapors when heated, to a distillto produce nitric acid, while constantly agitating the mass being treated and causing different portions of the same to be simultaneously presented in the form of separate films to permit of thefree escape of acid the surface thereof on said disc member in the form of a plurality of films and simultaneously subjecting the treated mass to a sufiicient temperature to effect. distillation of nitricvapors therefrom and recovering the acid vapors so evolved.

5. The method of making nitric acid which consistsin continuously disrupting a reacting mass comprising strong sulphuric acid and a nitrate by means of a plurality of cutting devices capable, of maintaining eli'ective agitation even when the mass assumesan incipient solid phase and presenting portions of such mass inthe form of a plurality of films on opposite side such cutting device, simultaneously subjecting the mass to asuflicienttemperature to distill the nitric acid vapors and recovering the nitric acid vapors so evolved.

6. The method of making nitric acid which consists insubjecting a charge, comprising strong sulphuric acid and a nitrate compound capable of reacting therewith to form-nitric acid to a temperature suflicient' to distill nitric acid as formed while constantly agitating the mixture and periodi cally presenting portions thereof in the form of thin layers above the normal surface of the mixture and then recovering the nitric acid vapors evolved.

swa

tact with freshly evolved nitric acid vapors passing to such condenser.

8. Theherein described apparatus com. prising an acid still having a vapor outlet, agitating means therein including a plurality of rotating discs andmeans for heating said still. i

9. The herein described apparatus comprising an elongated still having a longitudinal series of agitator discs rotatably mounted therein, certain of saiddiscs being provided with means ,for facilitating the elevation of liquid by said discs when the same are partially submerged in a charge of material being treated in said still, means for rotating said discs and means for heating said still.

10. The combination comprising a nitric acid still provided with disc-like means capable of revolving therein and adapted to agitate a charge being treated insaid still whether the same exists in a. liquid or a semi-solid phase and means for revolving said disc-like means.

11. The method of making nitric acid which consists in gradually mixing concentrated sulphuric acid with an alkali-metal nitrate while subjecting the mixture in a furnace to v a distilling temperature, said sulphuric acid, prior to admixture with said nitrate, being preheated by the waste. gases of such furnace, and consequently agitating the mass during such treatment.

12.The method of making nitric acid which consists in gradually mixing concentrated sulphuric acid with an alkali-metal nitrate while subjecting the mixture in ai'urnace to a. distilling temperature, said sulphuric acid, prior to admixture With said nitrate, being preheated by the Waste gases of such furnace and consequently agitating the mass during such treatment by causing several portions of the same to. be simultaneously presented in the form of separate films topermitof the free escape of acid 1 vapors therefrom at comparatively low temperatures andthen recovering the nitric acid evolved from such treatment.

Signed at Summit, in the county of Union and State of New Jersey, this 21 day of March, 1925.

' ARTHUR HOUGH. 

